Controlled deflation device for a gas bag

ABSTRACT

A device for venting a gas bag made of a textile material includes at least one ignitable pyrotechnic charge which is associated with the gas bag in such a way that, when the pyrotechnic charge is ignited, at least one thread of the textile material is directly destroyed by the explosion of the pyrotechnic charge.

FIELD OF THE INVENTION

The present invention relates to a device for venting an airbag,especially for venting an airbag in an active passenger restraint systemof a vehicle.

BACKGROUND OF THE INVENTION

In order to reduce the risks of injury for the vehicle passengers incase of a road accident, modem vehicles are increasingly often equippedwith an active passenger restraint system. Such an active passengerrestraint system comprises in general one or more airbags which are in aflash inflated in case of an impact of the vehicle and which take up theenergy released by the passenger during the impact.

As an airbag, such as a frontal airbag, exits the dashboard or thesteering wheel mounted module at very high speeds (200 to 300 km/h), foravoiding injuries of the passenger by the released airbag it isadvantageous to interrupt or control the complete inflating or unfoldingof the airbag as soon as the passenger has sufficiently immerged in theairbag and a sufficient pressure has built up in the airbag in order tobe able to securely take up the energy of the passenger. As the timewhen the passenger has sufficiently immerged in the airbag very stronglydepends on several parameters, such as the seat position of thepassenger at the time of the accident, the interruption of the inflatingprocess of the airbag can become necessary in any stadium of its releaseoperation.

As an inflating device functioning on the basis of pyrotechnics, aso-called inflator, cannot be interrupted in its function at anyarbitrary time due to the system, a passenger restraint systemconsequently has to comprise a device for purposefully venting theairbag for interrupting the release operation in a controlled manner.Such a device has to permit to deflate the gas blown into the airbag bythe inflator at any arbitrary time and to avoid a further inflation ofthe airbag.

From WO-A-98/01323, a device is known in which the gas bag comprises aventilation opening which Is closed at a frangible line or predeterminedbreaking line. The predetermined breaking line is designed to remainintact below a predetermined nominal pressure within the airbag and toautomatically break open above the nominal pressure under the influenceof the pressure. Such a predetermined breaking line is generallyachieved by a thoroughly and technically precisely dimensioned weakeningof the material employed. This weakening of the material can e.g. beeffected by a perforation in which small incisions are disposed alongthe provided predetermined breaking line. In another embodiment, thepredetermined breaking line is formed when closing the airbag by meansof a seam produced by sewing, the thread used for sewing and thedistance between the stitches being exactly mated to the demands of theairbag release. Alternatively, the airbag hull can also be closed bysealing, e.g. by ultrasonic sealing, with exactly adapted sealingpatterns. In this case, the sealing seam is the predetermined breakingline.

From the EP-A-638 466, an airbag is known in which certain areas of theairbag material are slightly permeable to gas at a normal workingpressure due to a purposeful weakening of the airbag material. Theseareas, the so-called dynamic vents, are for example formed byperforating the airbag material by means of a laser or by means of aneedle punch. At a critical gas pressure above the normal workingpressure, the gas escaping from the dynamic vents causes a melting orburning of the airbag material.

The problem with such predetermined breaking lines or dynamic vents,respectively, which automatically break open under the airbag pressure,is that due to the manufacturing tolerances an exact adjustment of therequired nominal pressure at which the predetermined breaking line orthe dynamic vent, respectively, breaks open is hardly possible.

A solution of this problem is to be found in controlled venting devices.

The document U.S. Pat. No. 5,899,494, for example, describes an airbagdevice in which the inflating device is connected with the airbag bymeans of a distributor. The inflating device and the distributor arearranged in a housing which is gas-tightly sealed at one side of theairbag. The distributor as well as the housing are provided with adeflagration device which can burn a vent into the distributor or thehousing, respectively, within a very short time after activation by anelectrical pulse.

A controlled venting device is also described in the document GB-A-2 306409. In this device, the airbag comprises a valve which is opened uponcontrol by an electric signal. In a first embodiment, the valvecomprises an expanded opening in the airbag material which is sealed bya sealing disc made of a meltable material. The disc comprises apredetermined breaking point with a reduced thickness to which apyrotechnic charge is assigned at a distance. If the pyrotechnic chargeis ignited by an electric signal, the same generates a flame which burnsthrough the disc material in the region of the predetermined breakingpoint. Subsequently, the sealing disc further cracks open along thepredetermined breaking point such that a fairly large vent is formed.

In another embodiment of the device from the GB-A-2 306 409, the airbaghas a two-layer design. In the region of the valve, one of the layerscomprises an opening which is sealed by a membrane formed by the secondlayer. A housing mounted at the airbag contains an ignitable pyrotechniccharge and a piston disposed between the pyrotechnic charge and themembrane and being provided with a cutting blade. By igniting thepyrotechnic charge, the piston is driven into the direction of themembrane, the cutting blade cutting the membrane, such that a vent iscut into the airbag.

SUMMARY OF THE INVENTION

Consequently, it is the object of the present invention to proposeanother device for purposefully venting a gas bag.

This object is solved according to the invention by a device for ventinga gas bag made of a textile material, especially an airbag, with atleast one ignitable pyrotechnic charge which is associated to the gasbag in a region such that, when the pyrotechnic charge is ignited, atleast one thread of the textile material is destroyed in the region ofthe pyrotechnic charge. The pyrotechnic charge is in this case arrangeddirectly at or in the textile material, so that, when the pyrotechniccharge is ignited, at least one thread of the textile material isdirectly destroyed by the explosion of the pyrotechnic charge. By thedestruction of at least one thread of the textile material, commonly awoven or knitted fabric, the textile material can crack open at therespective site. Under the influence of the gas pressure in the interiorof the gas bag, the textile material cracks further open at therespective site, so that a fairly large vent opening is formed throughwhich the gas flowing into the gas bag can escape. Thereby, a furtherinflation of the airbag is effectively suppressed. It should be notedthat the thread to be destroyed by the explosion is a “normal” thread ofthe textile material, e.g. a weaving or a knitting thread of the airbag,as well as a seam thread of a fastening seam formed by an appropriateproduction technique in the material of the gas bag, which thread isprovided especially for this purpose. As soon as the seam fiber isbroken at at least one site, the fastening seam can be opened withoutany expenditure of force if it is appropriately designed by specialweaving or knitting techniques, respectively, and so the vent openingcan be uncovered. It should further be noted that in case of acorresponding expansion of the pyrotechnic charge several threads of thetextile material can be destroyed simultaneously, so that the ventopening quickly reaches the desired size.

In contrast to the presently known devices, the device according to theinvention is actively triggered by igniting the pyrotechnic charge. Thismeans that the venting operation can be triggered at any time in anexactly controlled manner. The triggering of the venting device can, forexample, be effected by an airbag control module, after a sensor meanshas detected that a sufficient force or pressure level between theairbag and the passenger has been exceeded. The ignition of thepyrotechnic charge is preferably effected electrically, i.e. by anignition pulse or an ignition current which is applied to thepyrotechnic charge by the control device, e.g. the airbag control, viaconnection lines and which heats the same to a temperature above theignition temperature of the pyrotechnic charge.

Another advantage of the device according to the invention is that inthe airbag material no predetermined breaking point, i.e. no purposefulweakening, has to be provided. The mechanical strength of the airbagmaterial is accordingly not impaired before the present device istriggered. This is of a special importance as the folded airbag has tobe securely sealed in order to guarantee an inflation in case of animpact. In particular when manufacturing the airbag and mounting it intothe vehicle, the airbag has to withstand the deformations and loadsinvolved without being damaged, as a damage could reduce its properfunction over the required working life.

In a first possible aspect of the invention, the pyrotechnic charge isformed as an explosive thread which is introduced into the textilematerial of the gas bag or applied onto the textile material. Such anexplosive thread comprises, for example, an electrically conductivestranded wire which is surrounded by an explosive casing and/or into theinterweaving of which an explosive is introduced. Alternatively, theexplosive thread can comprise a thread made of electrically conductiveexplosive material.

The explosive thread can, for example, be directly interlaced or workedinto the textile material when manufacturing the airbag material.

In this manner, the explosive thread is an integral part of the textilematerial. Another possibility of introducing the thread is to sew theexplosive thread into the textile material after the manufacture of thesame. The explosive thread can, for example, serve as a seam thread withwhich a defined vent opening is sewn up. In contrast to introducing thethread into the textile material of the gas bag, the explosive threadcan also be applied onto the textile material e.g. by sewing it onto thetextile material.

In an alternative aspect, the pyrotechnic charge comprises a filamentand an explosive coating, the filament being introduced into the gas bagor applied onto the gas bag and the explosive coating being applied ontothe gas bag in the region of the filament. The filament can beintroduced into or applied onto the textile material according to one ofthe above described techniques or it is printed onto the textilematerial, e.g. by means of a known screening process. Subsequently, theexplosive is applied onto the textile material over the filament in anarbitrary additive process. If the filament is provided with an ignitioncurrent by a control module via connection lines, the filament, togetherwith the explosive provided thereabove, is heated to a temperature abovethe ignition temperature, so that the pyrotechnic charge is ignited andthe airbag is vented.

If the explosive to be applied onto the textile material is electricallyconductive, a filament can optionally be dispensed with. In this case,the pyrotechnic charge comprises an explosive coating made of anelectrically conductive explosive which is applied between twoconnection lines for the pyrotechnic charge onto the gas bag such thatthe explosive coating electrically contacts the two connection lines.When this pyrotechnic charge is provided with the ignition current, thenecessary heat for heating the explosive is generated in the explosivecoating itself.

It should be noted that all the above mentioned embodiments of thepyrotechnic charge comprise a continuous electrically conductive pathwhich is connected to the control module. Thereby, independent of therespective embodiment of the pyrotechnic charge, it becomes possible tocheck the same for its operativeness during the normal operation of thevehicle, that is when the airbag is not released. In fact, the controlmodule can check the integrity of the conductors by periodicallymeasuring the electric resistence of the continuous electricallyconductive path. If the measured resistence value comprises a greaterdeviation from a given reference value, e.g. a danger signal can showthe driver of the vehicle that the airbag device has to be checked fordefects in a workshop.

In a preferred aspect of the invention, the pyrotechnic charge isassociated to the gas bag at an inner side of the gas bag. In this case,the connection lines for the pyrotechnic charge will extend internallyof the airbag and a damage of the device from the outside is excluded.In this case, the pyrotechnic charge is advantageously arranged in aregion of the gas bag facing away from the passenger, such that the gasescaping from the formed vent opening does not blow against thepassenger. In this manner, an injury of the passenger by the particlesblown out together with the gas flow can be avoided.

It should be noted that the device for venting the airbag is preferablydesigned such that the total area of the ventilation openings in theairbag conditioned by the triggering of the device is larger than thetotal area of outlet openings of the airbag which permit an escape ofthe gas after the complete defolding of the airbag. Here, it is remindedthat the outlet openings provided in an airbag only serve for slowlyletting escape the gas pressure in the airbag after it has beencompletely inflated in order to permit a collapsing of the airbag.Accordingly, the total area of these outlet openings is not sufficientfor evacuating the gas amount flowing into the airbag when the gasgenerators are still working. By designing the ventilation openingscorresponding to their function to be larger than the outlet openings,it can be guaranteed that the gas flowing into the airbag can escapeafter the triggering of the venting device so quickly that a furtherinflation of the airbag can be avoided even if the gas generators arestill working.

In order to achieve a redundance in the system, preferably severalignitable pyrotechnic charges are arranged in parallel connection withcommon connection lines. The pyrotechnic charges can, for example, bearranged in parallel in the direction of the weaving thread. Thereby, itis avoided that the failure or the non-ignition of a charge leads to afailure of the whole system. Moreover, in this embodiment a quickeropening of the vent opening can be achieved as in case of an ignition ofthe thus arranged pyrotechnic charges the textile material is destroyedat several sites simultaneously.

It should be noted that it can also be advantageous to provide severalindependent ventilation means at various sites of the airbags. Apartfrom the redundance conditioned thereby, with such an embodiment adirectional venting is also possible by venting the airbag, for example,only in a region facing away from the passenger.

The connection lines for the ignitable pyrotechnic charges are, forexample, introduced into the gas bag and/or applied onto the gas bagwith one of the above described techniques. A possible production manneris the printing of the lines onto the textile material. This can, forexample, be effected in a screening process or any other appropriateprinting process.

In order to design a defined ventilation opening, the region of the gasbag where the pyrotechnic charge is associated to the gas bag ispreferably circumscribed by at least one seam. The cracking open of thetextile material initiated under the influence of the gas pressure inthe interior of the gas bag after the ignition of the pyrotechnic chargeis stopped at the surrounding seam, so that the formed vent opening hasa defined dimension. Thereby, it can be avoided that the opening whichis formed widens in an uncontrolled manner and the airbag undergoes atoo abrupt pressure drop as a consequence.

It should be noted that the above.described device for venting a gas bagis especially suitable for being employed in a so-called “intelligent”passenger restraint system for a vehicle. Such a passenger restraintsystem comprises, apart from the venting device, at least one airbagwith a control device and a sensor means for detecting a local pressureexerted on the passenger by the airbag. Here, the control deviceactivates the device for venting the gas bag based on a pressure signaldetected by the sensor means when a predetermined threshold value isexceeded and triggers the same. For doing so, the control deviceevaluates the position signal of the sensor means for example accordingto the pressure and/or time, i.e. according to the local pressure whichthe airbag exerts on the passenger or the time during which thispressure acts on the passenger.

In a particularly advantageous embodiment, the passenger restraintsystem comprises several devices for venting a gas bag which areassigned to the airbag in several regions, and the sensor meansadditionally detects the position of an impact region onto the airbag atwhich the airbag exerts a local pressure on the passenger. The controldevice activates in this case by means of a position signal detected bythe sensor means preferably the one of the devices for venting the gasbag which is essentially opposite the impact region with respect to theairbag. Such a design for example permits a directional venting byventing the airbag only in a region facing away from the passenger.

In an advantageous embodiment, the sensor means comprises at least onesensor which is arranged on the airbag in a region which faces thepassenger when the airbag is released. The sensor can for example be aforce sensor arranged on the airbag which takes up the pressure exertedon the passenger by the airbag and converts it into a correspondingelectrical signal. Such a force sensor advantageously comprises at leasttwo electrode structures which are applied onto a textile substrate at acertain mutual distance and a layer of a semiconductor material which isapplied over the electrode structures in an active region of the sensorin direct contact with the electrode structures, the layer of asemiconductor material comprising an inner resistance being variable inresponse to a deformation of the layer. The textile substrate cancomprise an arbitrary soft textile material. In a particularlyadvantageous, because simple, variant, the textile material comprisesthe actual airbag material, the electrode structures being directlyapplied to the airbag.

Such a sensor can dispense with stiff substrates as they are for exampleusual in common sheet pressure sensors. Thereby, the sensor has a veryhigh ductility, so that the sensor can be easily folded together withthe airbag. Moreover, the risk of an injury for the passenger by thesensor is largely excluded due to the softness of the sensor.

It should be noted that instead of the force sensor, a capacitivedistance sensor with at least one electrode structure arranged on theairbag or an inductive distance sensor with at least one inductive coilarranged on the airbag and connected to an alternating voltage can beused.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, various aspects of the invention are now describedwith reference to the enclosed Figures. In the drawings:

FIG. 1 shows a section of an airbag material with venting device;

FIG. 2 shows in an enlarged section of FIG. 1 the parallel connection ofthe various pyrotechnic charges;

FIG. 3 shows an alternative embodiment of the parallel connection;

FIG. 4 shows a section through the airbag material with the pyrotechniccharge applied thereon;

FIG. 5 shows a partial sectional view of the airbag material with thepyrotechnic charge applied thereon;

FIG. 6 shows an alternative embodiment of the pyrotechnic charges usingan electrically conductive explosive;

FIG. 7 shows another embodiment of a pyrotechnic charge;

FIG. 8 shows a section through the embodiment of FIG. 7;

FIG. 9 shows a diagram for arranging the venting device on the airbag.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In FIG. 1, a section of an airbag material 10 with a first embodiment ofa venting device 12 is represented. The venting device 12 comprisesseveral electrically ignitable pyrotechnic charges 14 which areinterconnected in parallel by common connection lines 16. The individualpyrotechnic charges with a (non-depicted) control module, preferably theairbag control module, which supplies an ignition current to theconnection lines 16 for triggering the device, are connected via theconnection lines 16.

The pyrotechnic charges 14 are applied onto the airbag such that, whenthe charges are ignited, at least one thread of the textile airbagmaterial is destroyed. Thereby, the woven or knitted fabric of thetextile material is destroyed such that it cracks further open under theinfluence of a gas pressure prevailing in the airbag and uncovers anopening. The cracking open of the textile material is effected in thedirection of the extension of the destroyed thread, so that by suitableweaving or knitting techniques a certain shape of the vent opening canbe caused.

In order to restrict the vent opening in its dimension, i.e. in order tolimit the cracking open of the airbag material to a certain length, theregion where the pyrotechnic charges 14 are applied onto the airbagmaterial 10 is preferably circumscribed by a reinforcing seam 18. Atthis seam 18, the crack forming in the airbag material is stopped in itsfurther extension and thus the size of the vent opening is limited. Inorder to further increase the security against an uncontrolled crackingopen, the surrounding seam 18 can also serve as a fastening seam foranother reinforcing element.

If the direction of the spreading of the formed crack in the airbagmaterial 10 is clearly defined, the critical region does in principlenot have to be completely sewn up. In this case, it suffices indeed toprovide two reinforcing seams which extend at the desired distance toone another transversely to the direction of the spreading of the crack.In practice, however, a complete sewing up of the critical region willbe preferred for safety reasons.

FIGS. 2 and 3 show, in an enlarged section of FIG. 1, variousembodiments of the parallel connection of the various pyrotechniccharges 14. Each pyrotechnic charge 14 comprises in the representedembodiment a filament 20 which is interconnected between the twoconnection lines 16 and contacts the same. The filament can beintroduced into the airbag material 10 or applied onto, the material 10,as represented. Subsequently, an explosive coating 22/22′ is appliedover the filament 20 onto the airbag material 10 and the filament 20.The explosive coating 22/22′ can here comprise a lateral dimension beinglarger than the corresponding dimension of the filament 20. Thereby, thethread of the airbag material to be destroyed is destroyed over agreater length when the device is ignited. In the direction of theextension of the filament 20, too, the extension of the crack in theairbag hull can be influenced by appropriately dimensioning theexplosive coating 22/22′. By an enlarged dimension of the explosivecoating in this direction (cf. FIG. 3), the width of the region to beblasted can be directly influenced.

FIGS. 4 and 5 show a possible arrangement of the various elements of thepyrotechnic charge 14 on the airbag material. The filament 20 can, forexample, be printed of conductive silver directly onto the airbag. Then,in an additive process, the explosive material 22″ is applied onto thisfilament 20 in its desired dimension.

An alternative embodiment of the pyrotechnic charges 14 using anelectrically conductive explosive is shown in FIG. 6. In thisembodiment, the pyrotechnic charge 14 comprises an explosive coating22′″ made of an electrically conductive explosive which is appliedbetween the two connection lines 16 for the pyrotechnic charge 14, suchthat the explosive coating 22′″, electrically contacts the twoconnection lines 16. When this pyrotechnic charge 14 is provided withthe ignition current, the necessary heat for heating the explosive isgenerated in the explosive coating itself.

A completely different embodiment of the pyrotechnic charge is shown inFIGS. 7 and 8. In this variant, the pyrotechnic charge 14 is formed asan explosive thread which is introduced into the textile material of thegas bag or applied onto the textile material. Such an explosive threadcomprises for example an electrically conductive stranded wire 24 whichis surrounded by an explosive casing 26. Alternatively, the explosivethread can comprise a stranded wire in the interweaving of which isintroduced an explosive or a thread made of electrically conductiveexplosive material.

The explosive thread can, for example, be directly interlaced or workedinto the textile material when the airbag material is manufactured. Inthis manner, the explosive thread becomes an integral part of thetextile material. Another possibility of introducing the thread is tosew the explosive thread into the textile material after the productionof the same. The explosive thread can, for example, serve as a seamthread with which a defined vent opening is sewn up. Such anintroduction of the explosive thread is shown in FIG. 9. FIG. 9accordingly shows a section of an airbag 10 in the region where twosections 112 and 114 of the airbag are sewn together. The two sections112 and 114 overlap in the shown region and are usually sewn to oneanother by a simple or multiple-row seam 116.

For generating an appropriate vent opening 118, the normal seam 116 isinterrupted over a certain length L in the present embodiment. Thelength L of the interruption of the seam 116 here corresponds to thedesired length of the vent opening.

In order to seal the airbag, the two sections 112 and 114 of the airbagare subsequently sewn to one another in the region of the interruptionof the normal seam 116 by means of one of the above described explosivethreads 120. When conducting an appropriate electric current through theexplosive thread 120, the same is heated up to a temperature above theignition temperature of the explosive, so that the explosive is ignitedand the seam 116 is destroyed.

In FIG. 10, the arrangement of the vent opening 12 on the airbag 10 isschematically shown. The vent opening 12 is, as shown, preferablyarranged in a region of the gas bag facing away from the passenger 28,such that the gas escaping from the formed vent opening does not blowagainst the passenger 28. In this manner, an injury of the passenger bythe particles blown out together with the gas flow can be avoided.

LIST OF REFERENCE NUMERALS

10 Airbag made of airbag material

12 Venting device

14 Pyrotechnic charges

16 Connection lines

18 Reinforcing seam

20 Filament

22 Explosive coating

24 Electrically conductive stranded wire

26 Explosive casing

28 Passenger

112, 114 Sections of the airbag

116 Multiple-row seam

118 Vent opening

120 Explosive thread

What is claimed is:
 1. A device for venting a gas bag made of a textile material, comprising at least one ignitable pyrotechnic charge which is associated to the gas bag in such a way that, when the pyrotechnic charge is ignited, at least one thread of the textile material is directly destroyed by the explosion of the pyrotechnic charge wherein said ignitable pyrotechnic charge is arranged in the textile material of said gas bag.
 2. A device for venting a gas bag made of a textile material, comprising at least one ignitable pyrotechnic charge which is associated to the gas bag in such a way that, when the pyrotechnic charge is ignited, at least one thread of the textile material is directly destroyed by the explosion of the pyrotechnic charge wherein the pyrotechnic charge is formed as an explosive thread, said explosive thread being introduced into the textile material of the gas bag or being applied onto the textile material of the gas bag.
 3. The device according to claim 2, wherein said explosive thread comprises an electrically conductive stranded wire, which is surrounded by an explosive covering.
 4. The device according to claim 2, wherein said explosive thread comprises an electrically conductive stranded wire having an explosive material introduced into an interweaving of individual strands.
 5. The device according to claim 2, wherein said explosive thread comprises a thread made of an electrically conductive explosive material.
 6. A device for venting a gas bag made of a textile material, comprising at least one ignitable pyrotechnic charge which is associated to the gas bag in such a way that, when the pyrotechnic charge is ignited, at least one thread of the textile material is directly destroyed by the explosion of the pyrotechnic charge wherein said pyrotechnic charge comprises a filament and an explosive coating, the filament being introduced into the gas bag or applied onto the gas bag and the explosive coating being applied onto the gas bag in the region of the filament.
 7. A device for venting a gas bag made of a textile material, comprising at least one ignitable pyrotechnic charge which is associated to the gas bag in such a way that, when the pyrotechnic charge is ignited, at least one thread of the textile material is directly destroyed by the explosion of the pyrotechnic charge wherein said pyrotechnic charge comprises an explosive coating made of an electrically conductive explosive and two connection lines, said coating being applied between said two connection lines onto the gas bag such that the explosive coating electrically contacts the two connection lines.
 8. A device for venting a gas bag made of a textile material, comprising at least one ignitable pyrotechnic charge which is associated to the gas bag in such a way that, when the pyrotechnic charge is ignited, at least one thread of the textile material is directly destroyed by the explosion of the pyrotechnic charge wherein the pyrotechnic charge is associated to the gas bag at an inner side of the gas bag.
 9. A device for venting a gas bag made of a textile material, comprising at least one ignitable pyrotechnic charge which is associated to the gas bag in such a way that, when the pyrotechnic charge is ignited, at least one thread of the textile material is directly destroyed by the explosion of the pyrotechnic charge wherein several ignitable pyrotechnic charges are arranged in a parallel connection with common connection lines.
 10. A device for venting a gas bag made of a textile material, comprising at least one ignitable pyrotechnic charge which is associated to the gas bag in such a way that, when the pyrotechnic charge is ignited, at least one thread of the textile material is directly destroyed by the explosion of the pyrotechnic charge wherein connection lines for the ignitable pyrotechnic charge are applied onto the textile material of said gas bag introduced into the textile material of said gas bag.
 11. A device for venting a gas bag made of a textile material, comprising at least one ignitable pyrotechnic charge which is associated to the gas bag in such a way that, when the pyrotechnic charge is ignited, at least one thread of the textile material is directly destroyed by the explosion of the pyrotechnic charge wherein a region of the gas bag, in which the pyrotechnic charge is associated to the gas bag, is circumscribed by at least one seam.
 12. A passenger restraint system for a vehicle, comprising at least one airbag made of a textile material, said airbag having at least one pyrotechnic charge associated therewith in such a way that, when the pyrotechnic charge is ignited, at least one thread of the textile material is directly destroyed by the explosion of the pyrotechnic charge inflator means for inflating said airbag a control device for controlling the deployment of said airbag, and sensor means for detecting a pressure exerted by the airbag on the passenger, wherein said control device triggers the ignition of said pyrotechnic charge based on a pressure signal detected by the sensor means when a predetermined threshold value is exceeded.
 13. The passenger restraint system according to claim 12, wherein the control device evaluates the pressure signal of the sensor means according to the pressure and/or time.
 14. The passenger restraint system according to claim 12, wherein the pyrotechnic charge is arranged on the airbag in a region which faces away from the passenger when the airbag is deployed.
 15. The passenger restraint system according to one of claim 12, wherein the pyrotechnic charge is designed such that the total area of ventilation openings in the airbag conditioned by the ignition of the pyrotechnic charge is larger than a total area of outlet openings of the airbag, which permit an escape of the gas after the complete defolding of the airbag.
 16. The passenger restraint system according to claim 12, wherein several pyrotechnic charges are associated to the airbag in different regions thereof.
 17. The passenger restraint system according to claim 16, wherein the sensor means further detects the position of an impact region on the airbag, where the airbag exerts a local pressure on the passenger, and wherein, based on a position signal detected by the sensor means, the control device triggers the ignition of a pyrotechnic charge, which is essentially opposite the impact region with respect to the airbag.
 18. The passenger restraint system according to claim 12, wherein the sensor means comprises at least one sensor, which is arranged on the airbag in a region which faces the passenger when the airbag is released.
 19. The passenger restraint system according to claim 18, wherein the sensor is a force sensor arranged on the airbag.
 20. The passenger restraint system according to claim 19, wherein said force sensor comprises at least two electrode structures, which are applied onto a textile substrate at a predefined distance, and a layer of a semiconductor material which is applied over the electrode structures in an active region of the sensor in direct contact with the electrode structures, the layer made of a semiconductor material comprising an inner resistance being variable in response to a deformation of the layer.
 21. The passenger restraint system according to claim 20, wherein the textile substrate comprises the airbag material, the electrode structures being directly applied onto the airbag. 